Recently, gold plating has been used for electronic equipment and electronic components because of gold's excellent electrical characteristics, and corrosion resistance, and especially, it has been widely used to protect the surface of the contact ends of the electronic parts. Gold plating has been used as the surface treatment for electrode terminals of semiconductor elements, or as a surface treatment for electronic components such as the connectors that connect the electronic equipment as well. Materials that use gold plating include, for example, metals, ceramics and semiconductors. The connectors used to connect electronic equipment use hard gold plating because of their utilization properties and require good corrosion resistance, wear resistance and electrical conductivity. Hard gold plating using gold/cobalt alloy plating and gold/nickel alloy plating have been known for a long time. Examples of such hard gold plating are disclosed in U.S. Pat. No. 2,905,601 and U.S. Pat. No. 4,591,415.
In general, electronic components such as connectors made from copper or a copper alloy. When gold is plated on copper or copper alloy, typically, nickel is plated on the copper or copper alloy surface as a barrier layer. The gold is then plated on the surface of the nickel plated layer. In general partial hard gold plating such as spot plating, plating with restricted surface and brush plating on electronic parts such as connectors is common. In the manufacturing process of these electronic components, plating is conducted by masking on the areas of electronic components where plating is not desired in order to restrict the amount of gold that is used since gold is very costly. However, when using conventional gold plating solutions, there is a problem that gold is deposited on the areas where gold is not needed. The solution of gold spreads along the surface of the object which is being plated, the gold solution spreads into the space between the mask and the object which is being plated, or the gold plates on the mask covering the portions of the object where plating is undesired.
In order to solve this problem, hexamethylene tetramine has been added to a hard gold plating solution such as disclosed in JP2008045194 patent publication published Feb. 28, 2008. However, this plating solution may be unstable. Accordingly, there is a need for an improved gold electroplating solution.